1. Field of the Invention
The present invention relates to an x-ray diagnosis apparatus having an X-ray plane detector.
2. Description of the Related Art
An X-ray diagnosis apparatus irradiates an X-ray on a target object and detects the X-ray transmitted through the target object, thereby obtaining the X-ray diagnosis image of the target object. As an X-ray detection system used for such an X-ray diagnosis apparatus, there is provided a screen film system, a computed radiography (CR) system using an imaging plate, an image intensifier-TV (II-TV) system using an image intensifier and a TV unit, or the like is used.
In recent years, an X-ray plane detector serving as an X-ray detection system bas received a great deal of attention because it has plural advantages, i.e., the portability of the screen film system or CR system, the high resolution of the screen film system, and the real-time properties of the II-TV system.
The X-ray plane detector comprises, for example, a phosphor for converting an X-ray into a light, a photodiode for converting the light into electric charges, a capacitor for accumulating the electric charges, and a TFT (Thin Film Transistor) serving as a switching gate for reading out the charges. One detection element comprises one photodiode, one capacitor, and one TFT. The X-ray plane detector is constituted by two-dimensionally arranging a plurality of such detection elements in accordance with the number of pixels.
In the conventional X-ray photography, a scattered X-ray removing grid is used to remove scattered X-ray components generated upon X-ray irradiation and acting on the photographed image. When a photographing operation is performed by an X-ray diagnosis apparatus to which the above-described conventional plane detector is applied, a Moire image, i.e., a kind of fixed pattern noise is generated in the photographed image.
As shown in FIG. 1, when the relationship between the pitch of image sensing pixels (e.g., a line of pixels along the data signal line), the pixels being represented by a square frame: a black dot represents the central portion of a pixel, and the period of the grid pattern, which generates a Moire, does not keep a steady positional relationship between the pixels and the fringe pattern, the waving phenomenon of amplitude variations having a long period (Moire phenomenon) is generated. Such a Moire image, i.e., noise must be removed from the image.